Edmonton, Alberta, Canada and Heidelberg Pharma, Ladenburg, Germany, November 4, 2025. Pacylex Pharmaceuticals Inc. (Pacylex) is a clinical-stage pharmaceutical company and world leader in developing N-myristoyltransferase inhibitors (NMTis) for cancer. Heidelberg Pharma AG (FSE: HPHA) is a clinical stage biotech company developing innovative Antibody Drug Conjugates (ADCs) for cancer. Oral zelenirstat is a potent NMTi under clinical investigation as a first-in-class targeted therapy for the treatment of hematologic cancers. Today, Pacylex announced that they teamed up with Heidelberg Pharma to test zelenirstat and PCLX-002 in ADCs and are jointly presenting their positive data at the 16th Annual World ADC, from November 3-6, 2025, in San Diego, California, USA. 

A poster with results from multiple breast and prostate cancer cell lines using different ADC targeting molecules and linkers will be presented on Nov. 4, 2025. The company’s CEO, Dr. Michael Weickert, will be available during the poster session and for one-on-one meetings. The details of the poster are below:

New payloads are needed for ADCs; only a very limited number of ADC payloads have entered clinical practice. NMT inhibitors have a unique mechanism of action that targets multiple processes critical to cancer cell growth and survival. The family of NMTis in development by Pacylex includes 28 with single-digit nM IC50s against human NMT1 which may be good ADC payloads. Zelenirstat, the first-in-class myristoylation inhibitor now in clinical development, was well tolerated as daily oral therapy in Phase 1 patients with refractory/relapsed lymphoma and refractory solid tumors. In studies reported here, zelenirstat was a potent payload in multiple different ADCs targeting breast and prostate cancer cell lines. Potency of zelenirstat ADCs against cancer cell lines was 20-fold to more than 1,000-fold higher than zelenirstat alone.

“We have shown that zelenirstat is not only active as an oral heme cancer drug, but by deploying it as payload on an ADC, we markedly improve its potency against solid tumor cells,” said Dr. Michael Weickert, CEO of Pacylex. “Given zelenirstat’s novel mechanism of action and clinical safety, we will aggressively explore it, and our other Pacylex molecules, as targeted ADC payloads.”

For more information:

Pacylex Pharmaceuticals Contact: Michael J. WeickertCEO, Pacylex Pharmaceuticals, Inc.E: michael.weickert@pacylex.comP: 650-218-1840Twitter @Pacylex (https://twitter.com/pacylex) LinkedIn (www.linkedin.com/company/pacylex-pharma)Facebook (https://www.facebook.com/pacylex)

About zelenirstat (aka PCLX-001 or DDD86481)

Zelenirstat (formerly identified as PCLX-001 or DDD86481) is a first-in-class, oral, small-molecule NMTi being developed to treat patients with leukemia, lymphoma, and for the treatment of solid tumors when used as a payload for ADCs. Zelenirstat selectively kills cancer cells in vitro and has been shown to regress hematologic malignancies and inhibit the growth of lung and breast cancer tumors in animal models. 

Pacylex completed and published a Phase 1 multiple ascending dose safety, tolerability, and pharmacokinetics study on zelenirstat in patients with relapsed/refractory lymphoma and refractory solid tumors (NCT04836195). Zelenirstat demonstrated an acceptable safety and tolerability profile, pharmacokinetics consistent with once-daily oral dosing, and early signs of efficacy. A clinical study in relapsed/refractory AML patients is accruing well (ClinicalTrials.gov ID NCT06613217).

About Pacylex Pharmaceuticals

Pacylex is the world leader in developing N-myristoyltransferase inhibitors (NMTis) as targeted therapies for the treatment of hematologic cancers and as payloads for antibody drug conjugates (ADCs) for solid tumors. Pacylex is conducting clinical studies of its lead drug, oral zelenirstat, the first and only clinically validated NMTi. The FDA has granted zelenirstat both Orphan Drug Designation and Fast Track Designation for AML. The US Department of Defense is supporting the initial clinical investigation of zelenirstat in AML patients. Pacylex is headquartered in Edmonton, Alberta, Canada, but also has an office in the San Francisco Bay area. The Cure Cancer Foundation, Alberta Cancer Foundation, and Alberta Innovates supported the initial clinical studies. For additional information, please visit www.pacylex.com.
About Heidelberg Pharma

Heidelberg Pharma is a biopharmaceutical company working on a new treatment approach in oncology and developing novel drugs based on its ADC technologies for the targeted and highly effective treatment of cancer. It is the first company to use the compound Amanitin from the green death cap mushroom in cancer therapy. The biological mechanism of action of the toxin represents a new therapeutic modality and is used as a compound in the Amanitin-based ADC technology, the so-called ATAC technology.

The company is based in Ladenburg, Germany, and is listed on the Frankfurt Stock Exchange: ISIN DE000A11QVV0 / WKN A11QVV / Symbol HPHA. More information is available at www.heidelberg-pharma.com

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